According to the previous studies, it has been reported that patients with ankylosing spondylitis (AS) may show spinal immobility caused by structural changes of the spine and restrictive ventilatory impairments with reduced vital capacity and chest expansion. We aimed to investigate the relationships among spinal mobility, pulmonary function, and structural change of the spine represented by vertebral squaring in patients with AS. We also planned to evaluate quality of life, disease activity, functional capacity, pain and fatigue, analyzing its relationships with other variables.

Thirty six adult patients with AS had been recruited from the Hospital for Rheumatic Diseases, Hanyang University Medical Center, Seoul, Korea. We examined participants’ spinal mobility through seven physical tests; 1) modified Sch?ber test, 2) lateral bending, 3) chest expansion, 4) wall to occiput, 5) finger to ground, 6) bimalleolar distance, and 7) range of motion (ROM) for cervical and thoracolumbar spine using inclinometer. Pulmonary function test (PFT) was performed with spirometer and forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and FEV1/FVC values were obtained. Vertebral squaring was also evaluated through the modified Stoke ankylosing spondylitis spinal score (mSASSS) of cervical and lumbar spine. Quality of life, disease activity, functional capacity, and fatigue were assessed by SF-36® Health survey (SF-36), the Bath ankylosing spondylitis disease activity index (BASDAI), the Bath ankylosing spondylitis functional index (BASFI) and the multidimensional assessment of fatigue (MAF) scale, respectively. Subjective physical condition and degree of pain were assessed by using 0 to 10 numeric rating scale. The Spearman correlation coefficient was used to check the correlation among variables.

The mean age of the participants was 34.5 ± 9.8 years. They showed decreased spinal mobility and restrictive pattern in PFT with reduced FEV1 (85.0 ± 13.7 %) and FVC (80.2 ± 15.4 %) and increased FEV1/FVC (109.1 ± 11.3). The mSASSS was negatively correlated with modified Sch?ber test, chest expansion, and ROM the spine, and positively correlated with lateral bending. Among the parameters related to PFT, FEV1 and FVC showed significant positive correlations with modified Sch?ber test, chest expansion, bimalleolar distance, and ROM of the spine, negatively correlated with finger to ground. Both FEV1 and FVC showed negative relationship with mSASSS, but the correlation between FEV1 and mSASSS was not statistically significant. However, FVC showed only statistically non-significant correlations with mSASSS. There were significant correlations between SF-36, BASDAI, BASFI, and MAF. The degrees of pain and perceptive physical condition were significantly related to SF-36, BASDAI, BASFI, and MAF, but showed no correlations with variables for spinal mobility, mSASSS, or PFT parameters except FEV1/FVC.

Our result shows that both spinal mobility and radiographic changes of vertebral body may have a predictive value for pulmonary impairment in AS patients, and it can be applied to predict pulmonary function in clinical settings. Pain and perceptive physical condition as well as musculoskeletal immobility or abnormalities in PFT have more important role on AS patients'' quality of life, functional capacity and fatigue. We suggest that providing appropriate pain management and advice to maintain proper physical activity level is important as improving spinal mobility or preventing structural changes of the spine.